Magnetic field extenders

ABSTRACT

An electron discharge device of the magnetic beam type which employs magnetic field extending means enabling the device to be provided with air-cooling features while reducing the magnetic gap.

United States Patent Inventor Wilton, Conn. 33,450

Apr. 30, 1970 Dec. 28, 1971 Appl. No. Filed Patented Assignee Jacob A. Randmer The Machlet Laboratories, Incorporated Springdale, Conn.

MAGNETIC FIELD EXTENDERS 7 Claims, 7 Drawing Figs.

U.S. 313/11, 313/153, 313/156, 313/160 Int. 1101] 7/24, H01j 1/50 Primary Examiner-Ronald L. Wibert Assistant Examiner-V. P. McGraw Attorneys-Harold A. Murphy and Joseph D. Pannone ABSTRACT: An electron discharge device of the magnetic beam type which employs magnetic field extending means enabling the device to be provided with air-cooling features while reducing the magnetic gap.

PATENTED DED28 is?! SHEET 3 OF 3 INVENTOR JACOB A. RANDMEH MAGNETIC FIELD EXTENDERS BACKGROUND OF THE INVENTION High power electron discharge devices of the magnetic beam power tube type have commonly employed water cooling for the dissipation of heat from the anode during the operation of the devices. These tubes are immersed in a mag netic field formed by an enclosing permanent magnet, which field is in the order of 500 to 1,000 Gauss for proper functioning. The water-cooling apparatus required only a comparatively small space in order to accommodate the water passages between the anode and the pole shoe faces of the magnet. In one type of tube, for example, a magnet gap of only 4 inches is required.

It is well known that the larger the gap is, the more magnetomotive force is required in order to force the necessary flux through the large gap. This of course requires a larger length of permanent magnet material. Also, as the gap is increased, the stray flux, that is, flux which is not useful in the device, increases and this usually requires a substantial increase in the permanent magnet cross section, as does an increase in the pole shoe face area.

While in water-cooled tubes relatively little space is required between the anode and the pole shoe faces for accommodating the cooling apparatus, air-cooled tubes require relatively large looking fins which extend a considerable distance from the anode. In this case the gap between the pole shoe faces can become very large. Typically, for an air-cooled version of the tube mentioned above, cooling fins of about two inches in width are required on each side of the anode. This requires a magnet gap of about 6.5 inches and an increase of the length of the permanent magnet part of the magnet of about 75 percent. The increase in stray flux may require a 50 percent larger magnet cross section. This leads to very bulky permanent magnet parts for the magnet which are relatively expensive.

SUMMARY OF THE INVENTION In accordance with this invention, means are provided in air-cooled magnetic beam tubes for reducing the effective magnet gap. This means comprises sheets of ferromagnetic material which are placed at selected intervals between the tins of the cooling radiator as field extenders which may be considered an extensions of the magnet pole shoes extending through the radiator to the anode. Since the permeability of ferromagnetic materials can be easily 1,000 to 100,000 times higher than the permeability of air or vacuum, or than that of the paramagnetic materials of the tube structures, such as copper, the sheets or field extenders may be made very thin and may, in fact, replace some of the fins of the radiator.

Thus, there is produced an air-cooled magnetic beam power tube wherein the effective magnet gap is reduced to a dimension which approximates the width of the anode and wherein no requirement exists for additional permanent magnet material length or cross-sectional size.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings, wherein:

FIG. 1 is an elevational view partly in axial section of an electron discharge device of a type with which the invention is adapted for use:

FIG. 2 is a transverse sectional view taken substantially on line 22 of FIG. I;

FIG. 3 is a transverse sectional view through the finned radiator of the tube shown in FIGS. 1 and 2, showing in detail one method of mounting a field extender:

FIG. 4 is a fragmentary side elevational view of the field extender shown in FIG. 3:

FIG. 5 is a sectional view taken on line 55 of FIG. 4; and

FIGS. 6 and 7 are views similar to FIG. 3 showing other manners of mounting field extenders.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to the drawings, the magnetic field extenders of this invention are adapted for use particularly with an air-cooled high power electron discharge device such as the magnetic beam power tube shown in FIGS. I and 2. This tube comprises an evacuated envelope [0 which includes a hollow cup-shaped metal anode l2 sealed at its open end to one end of a hollow cylindrical ceramic or other dielectric housing portion 14. The other end of the envelope portion 14 carries the terminal portion of the envelope including a pair of metal ring cathode tenninals I6 and 18 which are spaced from each other and from a grind terminal ring 20 by dielectric rings 22 and 24 of ceramic or the like. The envelope and electrode structures are conventional and well known, and therefore are not described in great detail herein.

Simply, the cathode terminal 16 may support one end of a column 26 which extends into the interior of the envelope portion 14, the column having a first transversely extending deck 28 secured to its inner end as shown. A second transversely extending deck 30 is located inwardly of or below, as seen in FIG. 1, deck 28 and is supported by one end of support members 32, the other end of members 32 being suitably connected to the second cathode terminal 18.

The cathode electrode comprises a planar array of filaments 34 which are hairpin-shaped and which are each mounted with one end fixed in deck 30 and with the other end passing freely through a respective hole in deck 30 and mounted in deck 28. Thus, a circuit is completed from a suitable source SC of filament current through terminal I6, column 26 and deck 28 into one side of the filaments, and out the other side through deck 30, support members 32 and terminal 18 in the well-known manner.

The filaments 34 extend into the interior of the anode l2 and are adapted, when suitable potentials are applied, to emit electrons toward the anode. To assist in this function, a grid is interposed on opposite sides of the cathode between the filaments and the anode walls. The grid comprises a plurality of grid wires 34 which are located opposite and between respective adjacent filament strands and parallel thereto as shown best in FIG. 2. Each end of the arrays of grid wires is secured to a respective metal loop or frame 38 and 38a which maintains the wires 36 in proper relative locations. Frame 38 is mounted on one end of a pair of grid support members 40, the other ends of which are connected in any suitable manner to grid terminal 20. Thus, when electrons pass from the cathode filaments 34 toward the anode 12, they flow into the influence of the grid potential field, which thereby accelerates the movement of the electrons toward the anode.

The present invention is particularly concerned with the utilization of a magnetic field to assist in properly directing the flow of electrons to the anode without permitting uncontrolled impingement of the electrons upon the grid wires. Such electron bombardment of grid elements will cause the production of undesired grid current. This problem and a method of solving it are fully set forth in US. Pat. No. 3,365 ,60l which is assigned to the same assignee as the present invention. The solution disclosed in the referred-to patent embodies the use of a magnet having pole pieces or pole shoe faces on opposite sides of the anode and parallel thereto for creating a magnetic flux which extends in the direction of electron flow and forms the electrons into beams or streams which are directed toward and pass to the anode without substantial impingement of the electrons upon the grid wires.

To achieve the best results it is desirable that the magnet -shoe faces be located relatively close to the anode so that the section, as does an increase in the pole shoe face area. The field required for a tube of the character described herein is in the order of 500 to 1,000 Gauss.

For water-cooled tubes, relatively little space is required between the anode and the pole shoe faces for accommodating the water passages of the cooling equipment. However, air-cooled tubes require a much larger space in which to position a radiator. Radiators of the type desired employ a number of relatively large fins which are attached to the outer surface of the anode and may extend a considerable distance from the anode. In such air-cooled devices the magnet gap necessarily becomes quite large. In one exemplary magnetic beam tube employing water cooling, the magnet gap is about 4 inches. However, when the same tube is provided with a finned radiator for air-cooling purposes, the cooling fins extend about 2 inches from each side of the anode, thus necessitating a magnet gap of about 6.5 inches. This would require an increase in permanent magnet material length of about 75 percent, and the increase in stray flux would require a 50 percent larger cross section of this magnet material.

Therefore, in accordance with this invention there is provided means which extends the magnetic field and effectively shortens the magnet gap so that a relatively small piece of permanent magnet material having large pole shoes and a large magnet gap may be efficiently utilized in air-cooled tubes. Referring to FIG. 2, it will be seen that the broad outer surfaces of the anode 12, those outer surfaces opposite the arrays of grid wires 36, are provided with outwardly extending fins 42, preferably of copper, which are brazed or otherwise mounted directly upon the anode by means assuring good heat transfer. The fins 42 extend longitudinally of the anode and are spaced sufficiently to permit a flow of forced cool air to pass between fins, thereby dissipating from the fins excess heat which has been conductively transferred thereto from the anode. The fins 42 may be located to extend transversely of the anode if desired, instead of longitudinally, without affecting the beaming in the tube. The choice is dictated by air flow considerations and air distributor design. A magnet 44 using a permanent magnet material piece 44a is positioned so that its pole pieces 46 and 48 which are made of soft iron are located perpendicular to the free ends of the fins 42 as shown, with their pole shoe faces 50 and 52 respectively located adjacent the ends of the fins.

In order to effectively reduce the excessive gap size, that is, the distance between shoe faces 50 and 52, fins or sheets of ferromagnetic material such as iron are placed in the radiator structure. For example, every fourth fin 42, in the structure shown in FIG. 2, is replaced by a ferromagnetic fin 54 which becomes a magnetic field extender." These magnetic field extenders may be brazed directly to the anode as shown, or may be mounted in other manners such as will be described later herein.

The field extenders 54 can be relatively thin because the permeability of ferromagnetic materials can be easily 1,000 to 100,000 times higher than the permeability of air or vacuum, or of the paramagnetic materials of the tube structure, such as copper. For instance, grain oriented transformer steel sheet has a relative permeability of 40,000 at 6,000 Gauss (see Henney Radio Engineers Handbook, 1959, pages 332). Generally, the field extenders 54 can be considered as extensions of the pole shoes through the radiator to the anode.

The space between field extenders may be relatively large since the magnetic field spreads at the end of each extender at the anode and becomes sufficiently uniform in the tube for beaming purposes. This is illustrated by the dotted lines in FIG. 2 which depict the approximate path of flux lines between opposing field extenders.

The field extenders may be designed as part of the radiator and may take on any of various forms. They may be secured, as by brazing or the like, directly upon the anode surface as shown in FIG. 2. In this case they may be located between cooling fins 42 or may replace specified cooling fins, as desired. They may be insertable between fins and attached to one of the fins as shown in FIGS. 3, 4 and 5, for example. Here one of the fins 42 is provided with at least one tab 56 located at at least one end thereof and a field extender 54a is slid between opposed edge flanges 58 on fin 42 to a position where the tab 56 may be bent into overlying relation to the adjacent end of the field extender to hold the extender in place. A plurality of such tabs may be employed with each field extender if desired.

In FIG. 6 a field extender 54a is shown as being secured between two adjacent fins 52 by a layer 62 of a suitable heat resistant epoxy cement.

in FIG. 7 a field extender 540 comprises a laminated structure or sandwich consisting of a layer of copper between two layers of iron, or a layer of iron between two layers of copper.

The field extenders must be well fastened to the anode or the cooling fins, otherwise they will be pulled out of position by the magnetic field and adhere to the pole shoes, which will lead to difficulties when a tube is inserted into or removed from a magnet. However, if convenient assembly techniques are employed, the field extenders may be designed as parts of the pole shoes of the magnet. Also, the field extenders should be relatively thin. They can easily be designed in such a way that the additional magneto motive force needed to drive the flux through the air cooling radiator is very small compared to what would be required if no field extenders were used. As a matter of fact, since the field extenders can terminate directly on the outer anode surface, the efiective magnet gap and, hence, the permanent magnet part of the magnet may be even smaller than for water-cooled tubes.

The effectiveness of the field extenders can be illustrated by determining the efi'ective gap for the tube referred to hereinbefore. Without field extenders the magnet gap is about 6.5 inches. With field extenders the effective gap is reduced to about 2.4 inches, obtained by the following design:

Field extenders of 0.040 inch thickness are interspersed at fiinch intervals between the copper fins. If the flux density is 700 Gauss in the cathode plane, then the fiux density in the fins will be 7000.500 inch/0.040 inch)=8,750 Gauss. Total flux through the entire magnetic path should remain approximately the same in order to retain the 700 Gauss in the tube. Assume that the field extenders are made of core iron which is low carbon electric furnace melted iron for relay cores and similar components. The permeability for this iron is about 2,500 at a flux density of 9,000 Gauss (see for instance pamphlet by Carpenter Steel Co. on Carpenter Alloys for electronic, magnetic and electrical applications, data for Carpenter Core lron). Therefore, the reluctance of the 4 inches gap portion taken up by the copper fins (2 inches on each anode side) is reduced to the reluctance of an equivalent air gap of 4 inches/2,500=0.0016 inch, or practically nothing. The effective gap becomes, therefore, somewhat larger than the anode thickness in order to provide clearances for insertion, space for aid ducts and/or nonmagnetic spacers, which may be needed to simplify insertion and removal of the tube from the magnet. lf Alnico V is used for the permanent magnet part of the magnet, a 4 inches to 5 inches long Alnico V- piece is sufficient to product a flux density of 700 Gauss in the tube. The magnet length for a water-cooled tube is 9 inches. A radiator of the approximate dimensions mentioned above is sufficient to provide a plate dissipation of 25 to 30 kw. in an air-cooled tube.

From the foregoing it will be apparent that all of the objectives of this invention have been achieved by the invention shown and described. It is to be understood, however, that various modifications and changes may be made by those skilled in the art without departing from the spirit of the invention as expressed in the accompanying claims. Therefore, all matter shown and described is to be interpreted as illustrative and not in a limiting sense.

I claim:

I. An electron discharge device of the magnetic beam type comprising a gas tight envelope having an annular anode as a part thereof, electrodes within the anode including a cathode for directing electrons radially toward the anode along paths perpendicular to the axis of the anode, a heat exchanger encircling the anode and comprising a plurality of spaced radially extending fins, a magnet having pole pieces on opposite sides of the anode adjacent outer ends of said fins for creating a magnetic fieid therebetween perpendicular to the axis of the anode and parallel to said fins and defining an actual magnet gap between pole pieces, and means for creating an effective magnet gap which is smaller than said actual magnet gap.

2. An electron discharge device as set forth in claim 1 wherein said means comprises at least one ferromagnetic element disposed between and parallel to two adjacent fins for extending the magnetic field through the heat exchanger into the envelop.

3. An electron discharge device as set forth in claim 1 wherein said means comprises a plurality of sheets of ferromagnetic material each of which is positioned between selected adjacent fins and parallel thereto for extending the magnetic field through the heat exchanger into the envelope.

4. An electron discharge device as set forth in claim 3 wherein said sheets are each located upon and parallel to a surface of a respective fin. each of said respective fins having at least one end tab bent to overlie an adjacent end of the associated sheet for retaining it in place.

5. An electron discharge device as set forth in claim 3 wherein said sheets are each adhesively secured to a respective fin.

6. An electron discharge device as set forth in claim 1 wherein said means comprises a plurality of field extenders located between selected adjacent fins and parallel thereto for extending the magnetic field through the heat exchanger into the envelope, said field extenders each comprising a sheet of ferromagnetic material laminated between said adjacent fins.

7. An electron discharge device as set forth in 'claim I wherein said means comprises a plurality of field extenders located between selected adjacent fins for extending the magnetic field through the heat exchanger into the envelope. said field extenders each comprising a pair of sheets of ferromagnetic material laminated upon opposite surfaces of a respective fin.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Inventor(s) Jacob A flandmer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

At [73] change MMachlet" to Machlett Column 1, line 27, delete "looking" and insert cooling-P Column line 13, delete "grind" and insert grid Column line 9, change "54a." to 54b Column Column 4, line 38., "7000" should read ZOO 4 line 57, change "product" to produce Column line 14, claim 2, change "envelop." to

-- envelope.

Signed and sealed this 15th daY f Me (SEAL) Attest:

EDWARD M. FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM 30-1050 069) USCOMM-DC 603'l6-P69 Y U45. GOVERNMENT PRINTING OFFICE l95 0-356!!! 

1. An electron discharge device of the magnetic beam type comprising a gas tight envelope having an annular anode as a part thereof, electrodes within the anode including a cathode for directing electrons radially toward the anode along paths perpendicular to the axis of the anode, a heat exchanger encircling the anode and comprising a plurality of spaced radially extending fins, a magnet having pole pieces on opposite sides of the anode adjacent outer ends of said fins for creating a magnetic field therebetween perpendicular to the axis of the anode and parallel to said fins and defining an actual magnet gap between pole pieces, and means for creating an effective magnet gap which is smaller than said actual magnet gap.
 2. An electron discharge device as set forth in claim 1 wherein said means comprises at least one ferromagnetic element disposed between and parallel to two adjacent fins for extending the magnetic field through the heat exchanger into the envelop.
 3. An electron discharge device as set forth in claim 1 wherein said means comprises a plurality of sheets of ferromagnetic material each of which is positioned between selected adjacent fins and parallel thereto for extending the magnetic field through the heat exchanger into the envelope.
 4. An electron discharge device as set forth in claim 3 wherein said sheets are each located upon and parallel to a surface of a respective fin, each of said respective fins having at least one end tab bent to overlie an adjacent end of the associated sheet for retaining it in place.
 5. An electron discharge device as set forth in claim 3 wherein said sheets are each adhesively secured to a respective fin.
 6. An electron discharge device as set forth in claim 1 wherein said means comprises a plurality of field extenders located between selected adjacent fins and parallel thereto for extending the magnetic field through the heat exchanger into the envelope, said field extenders each comprising a sheet of ferromagnetic material laminated between said adjacent fins.
 7. An electron discharge device as set forth in claim 1 wherein said means comprises a plurality of field extenders located between selected adjacent fins for extending the magnetic field through the heat exchanger into the envelope, said field extenders each comprising a pair of sheets of ferromagnetic material laminated upon opposite surfaces of a respective fin. 